When it is desirable for liquid formulations containing solid particulate matter to be homogeneous, it may be necessary that the individual particles of the solid particulate matter be finely-divided or "powdery". However, liquid formulations containing this sort of solid particulate matter may quickly stratify and/or agglomerate, with the result typically being the settling-out of the particulate material. Or the liquid formulation may exhibit still other undesirable aspects of instability such as precipitation of agglomerated or individual particles.
To provide desired shelf-life or stability, it is often necessary to include certain stability-enhancing additives or dispersants--such as certain natural gums, certain minerals, or certain water-soluble polymers--to these sorts of liquid formulations. Carboxymethyl cellulose, polyvinyl alcohol, and certain vinyl polymers (e.g. "CARBOPOL") are illustrative of certain water-soluble polymers that can be utilized as dispersants in this regard. Suitable, illustrative natural gums include arabic, guar, karaya, and tragacanth. (See, e.g., page 513 of The Condensed Chemical Dictionary, 10th edition, published in 1981 by Van Nostrand Reinhold Co.) Suitable, illustrative minerals include "Jeweller's Rouge", which is a mineral-art term that is understood to mean either fine, calcined ferric oxide or "haematite." (See, e.g., page 390 of the Handbook of Chemical Synonyms and Trade Names, 8th edition, published in 1978 by the CRC Press, Inc.) "Haematite", in turn, is a mineral-art term that is understood to refer to certain varieties of naturally-occurring, anhydrous ferric oxide. (See, e.g., page 343 of the Handbook of Chemical Synonyms and Trade Names, 8th edition.)
The use of particulate dispersants (such as the above-noted) to produce "stable" emulsions containing finely-divided particles can result in a number of undesirable side effects, however. For example, the natural gums as well as certain water-soluble polymeric dispersants may typically leave a "gummy" residue that can readily attract dirt. Moreover, the "Jeweller's Rouge" can be difficult to remove and thus may give rise to unsightly discoloration if left on a particular substrate surface over an extended period of time.
Other naturally-occurring minerals that can be used as dispersants, to produce so-called "stable" emulsions include, e.g., attapulgite, bentonite, clay, and fuller's earth. (See, e.g., pages 95, 115, 255, and 481, respectively, of the The Condensed Chemical Dictionary, 10th edition.) Naturally-occurring minerals of these sorts, however, typically may leave an unsightly or otherwise undesirable "scum" on a particular surface.
Thus to achieve overall acceptability for a wide variety of consumer and industrial uses, it is desirable to be able to produce stable liquid formulations without resorting to the inclusion of those sorts of stability-enhancing additives or dispersants mentioned hereinabove.
Yet it is particularly desirable that a wide variety of such liquid formulations--i.e., those which do not include the sorts of stability-enhancing additives or dispersants that are mentioned hereinabove--not only contain finely-divided particles homogeneously-dispersed throughout but that such liquid formulations also possess desirable shelf-life and other desirable "stability" qualities as well.